1. Field of the Invention
The present invention relates to a substrate for a liquid discharge head, which is used for a liquid discharge head.
2. Description of the Related Art
An ink jet head for discharging an ink is known as a liquid discharge head for discharging a liquid.
The ink jet head employs a method of providing a through slot (ink supply port) in a substrate having a device for generating an ink discharge pressure formed thereon, and supplying an ink from a face in an opposite side of a face having the device for generating the ink discharge pressure formed thereon.
As for a method for forming the ink supply port of such an ink jet head, a method is disclosed which combines a technique for patterning a protection film with the use of a photolithographic process with an anisotropic etching technique. U.S. Pat. No. 6,143,190 discloses a method for forming a supply port by the steps of: forming a protection film on a rear surface of a silicon (100) substrate; removing the protection film at a portion for forming the ink supply port therein with the use of the photolithographic process; and anisotropically etching the silicon substrate in a strong alkaline solution. This method has an advantage that the dimension of the supply port can be set according to the application, because the method can determine the dimension of the supply port by changing the dimension of an opening of the protection film on the rear surface.
However, this type of a method for forming the ink supply port has a problem of needing an increased number of processes and having low production efficiency, because of opening the protection film with the use of the photolithographic process. When employing a thermal oxide film as the protection film, the method results in needing a plurality of processes such as a process of forming the thermal oxide film, a process of applying a resist on the thermal oxide film, a process of exposing and developing the resist, a process of removing the thermal oxide film with the use of a wet etching or dry etching technique and a process of removing the resist.
In order to cope with the problem, U.S. Pat. No. 6,563,079 discloses a method of preparing a supply port without using photolithography. This method forms a supply port by the steps of: forming a protection film on a silicon substrate; forming one hole (hereafter referred to as a laser hole) or a plurality of laser holes aligned in one row by irradiating a portion at which the supply port is formed, with a laser light from above the protection film; and spreading the laser holes with an anisotropic etching technique. The method can progress the anisotropic etching without removing the protection film with the use of the photolithographic process, because an etchant invades into the silicon substrate from the laser hole. However, according to the method, the dimension of the removed protection film becomes approximately the same as the dimension of the laser hole, and accordingly the supply port formed after having been anisotropically etched results in acquiring approximately the same width of the opening on the rear surface of the silicon substrate as the dimension of the laser hole. Therefore, the method cannot form the supply port having a desired dimension, which is different from a process that is described in U.S. Pat. No. 6,143,190 and uses the photolithography. It is possible to increase the dimension of the supply port by enlarging the laser hole. However, when a hole is formed by using the laser, generally, as the spot size is increased, energy density per unit area decreases and machining capacity decreases. Therefore, the method may cause problems that a tact time for the machining increases, the hole occasionally cannot be dug on the way, and a machined shape is deformed in some cases.
However, it has been difficult in a conventional method for manufacturing an ink supply port of an ink jet head to form the ink supply port having high reliability in supplying an ink without increasing the number of processes.